Optical head device and optical information apparatus using this optical head device, and computer, optical disk player, car navigation system, optical disk recorder and optical disk server using this optical information apparatus

ABSTRACT

Providing an objective lens with a large numerical aperture (NA), the present invention records or plays conventional optical disks such as CDs and DVDs at high light usage efficiency, using an optical head capable of recording or reproducing high-density optical disks. A diffraction optical element ( 8 ) is disposed in a light path of a first light beam of a first wavelength λ 1  (400 nm to 415 nm) and a second light beam of a second wavelength λ 2  (650 nm to 680 nm). And, the present invention principally emits 5th order diffracted light with respect to the first light beam, and principally emits 3rd order diffracted light with respect to the second light beam, from the diffraction optical element ( 8 ). Thus, a high diffraction efficiency of substantially 100% can be obtained with respect to both wavelengths.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 11/565,190,filed Nov. 30, 2006, which is a Division of application Ser. No.10/504,375, filed Aug. 12, 2004, which is a National Stage applicationof PCT/JP03/01291, filed Feb. 7, 2003, which applications areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to optical head devices for the purpose ofrecording information onto optical information media such as, forexample, optical disks or optical cards and for reproducing or erasinginformation recorded onto the optical information media, relates tooptical information apparatuses in which these optical head devices areused, and to various systems in which these optical informationapparatuses are applied.

BACKGROUND ART

Optical memory technology that uses optical disks that have pit-shapedpatterns as high-density, large-volume memory media is gradually beingapplied widely to and entering general use in digital audio disks, videodisks, document file disks and also data files. Thus, the functions forusing a minutely narrowed light beam to successfully achieve recordingonto and reproduction of information from an optical disk with highreliability, are divided into three main functions, that is, a focusingfunction which forms a minute spot at the diffraction limit on theoptical disk, focus control (“focus servo”) and tracking control of theoptical system, and pit signal (“information signal”) detection.

With recent advances in optical system design technology and theshortening of the wavelengths of the semiconductor lasers serving aslight sources, the development of optical disks containing volumes ofmemory at greater than conventional densities is progressing. As anapproach towards higher densities, problems such as an increase in theaberrations due to slanting of the light axis (what is known as “tilt”)were found when investigating an increase in the optical disk sidenumerical aperture (NA) of the focusing optical system that focuseslight beams onto the optical disk. That is to say, the amount ofaberration which occurs with respect to the tilt increases when the NAis increased. It is possible to prevent this by thinning down thethickness (substrate thickness) of the transparent substrate of theoptical disk.

The substrate thickness of a Compact Disc (CD), which can be considereda first generation optical disk, is approximately 1.2 mm, and theoptical head device for CDs uses a light source emitting infrared light(with a wavelength λ3 that is 780 nm to 820 nm, with 800 nm as standard)and an objective lens with an NA of 0.45. Furthermore, the substratethickness of a Digital Versatile Disc (DVD), which can be considered asecond generation optical disk, is approximately 0.6 mm, and the opticalhead device for DVDs uses a light source emitting red light (with awavelength λ2 that is 630 nm to 680 nm, with 650 nm as standard), and anobjective lens with an NA of 0.6. Moreover, the substrate thickness of athird generation optical disk is approximately 0.1 mm, and the opticalhead device for these disks uses a light source emitting blue light(with a wavelength λ1 that is 390 nm to 415 nm, with 405 nm asstandard), and an objective lens with an NA of 0.85.

It should be noted that in this specification, “substrate thickness”refers to the thickness from a surface of the optical disk (or theoptical recording medium) on which the light beam is incident, to theinformation recording surface. As described above, the substratethickness of the transparent substrate of the high-density optical disksis set to be thin. From the view point of economy and the space that isoccupied by the device, it is preferable that an optical informationapparatus can record and reproduce information from a plurality ofoptical disks having differing substrate thicknesses and recordingdensities. However for this, it is necessary to have an optical headdevice provided with a focusing optical system capable of focusing alight beam up to the diffraction limit onto a plurality of optical diskshaving differing substrate thicknesses.

Furthermore, if diffracting optical elements are used as the opticalelements for constituting optical head devices, instead of therefracting optical elements such as lenses and prisms that are usuallyused, then the optical head devices can be made smaller, slimmer, andlighter.

Diffraction optical elements are optical elements that function byeffectively utilizing the diffraction effect of light, and arecharacterized by corrugations of a depth that is in the order of thewavelength, or by having a refractive index distribution or amplitudedistribution that is formed periodically or quasi-periodically on thesurface. It is known in the art that if the period of the diffractionoptical element is sufficiently large compared to the wavelength, thenit is possible to raise the diffraction efficiency to substantially 100%by making the cross section saw tooth-shaped.

However, if the frequency is sufficiently large compared to thewavelength, then the diffracting efficiency of the diffraction opticalelement reaches 100% only with respect to the design wavelength.Generally, the diffraction efficiency steadily decreases as thewavelength diverges from its design value. Consequently, if diffractionoptical elements are used in optical head devices in which light sourcesof a plurality of wavelengths are mounted so as to handle a plurality ofvarieties of optical disks, then the diffraction optical elements needto be optimally designed for each wavelength and disposed only in thelight path of the wavelength thereof in order to raise the lightutilization ratio.

A configuration whose object is to provide an optical head with highlight usage efficiency, which has a light source of a plurality ofwavelengths and diffraction optical elements that can handle a pluralityof different varieties of information recording media, is disclosed inJP 2001-60336A (first conventional example). The first conventionalexample is described below with reference to FIG. 10.

FIG. 10 is a lateral view of the basic configuration and the state oflight transmission of an optical head device according to the firstconventional example. As shown in FIG. 10, in the optical head device ofthe first conventional example, a collimator lens 71 and an objectivelens 18 are disposed in the light path from a laser light source 105 tothe information recording medium such as a high density optical disk 9or optical disk 11 such as a CD. The laser light source 105 is a lightsource that can selectively emit a first light beam of a firstwavelength λ1, and a third light beam of a third wavelength λ3, whichhas a wavelength substantially twice that wavelength. It should be notedthat in the description below, wavelengths in the region of 660 nm arealso considered, so that these are described as “second wavelengths”. Alaser light 205 that is emitted from the semiconductor laser lightsource 105 is converted to substantially parallel light by thecollimator lens 71 after which its light axis is bent by a mirror 20.The light beam 205 whose light axis was bent by the mirror 20 is focusedby the objective lens 18 onto the optical disk 9 or 11. The firstwavelength λ1 of the first light beam that is emitted by the laser lightsource 105 satisfies, for example, the relationship 350 nm≦λ1≦440 nm,and its focal spot can be brought to a minute point by provision of thelaser light source 105 that emits the first light beam of the firstwavelength λ1. Furthermore, the third wavelength λ3 of the third lightbeam that is emitted by the laser light source 105 satisfies, forexample, the relationship 760 nm≦λ3≦880 nm, and optical disks such asCDs and CD-Rs can be read out by provision of the laser light source 105that emits the third light beam of the third wavelength λ3. In thismanner, in the optical head device of the first conventional example,the wavelength of the light that is emitted is determined according tothe type of optical disk that is to be read out, and a light beam ofthat wavelength is emitted selectively.

Furthermore, in the optical head device of the first conventionalexample, a diffraction optical element 85 is disposed in the light pathbetween the mirror 20, which bends the light axis, and the objectivelens 18, for the purpose of correcting chromatic aberrations of theobjective lens 18. Here, the objective lens 18 and the collimator lens71 are aspherical lenses.

As described above, the diffraction optical element generally shows ahigh diffraction efficiency with respect to the design wavelength, butthe diffraction efficiency gradually decreases as it diverges from this.Consequently, when the diffraction optical element is disposed in thelight path is passed by both the light beam of the design wavelength andlight beams other than this, the diffraction efficiency deteriorateswith respect to one of the wavelengths.

However, if the period of the diffraction optical grating issufficiently large compared to the wavelength, then when the wavelengthis approximately half the design wavelength, the first order diffractionefficiency is substantially 0, but the second order diffractionefficiency is exceptionally high at substantially 100%.

In the first conventional example, an optical head device is disclosedin which, in a two wavelength optical head device that is capable ofhandling both high density optical disks that use a blue light sourceand optical disks such as CDs and CD-Rs, setting the relationship of thewavelength size of the two wavelengths to be approximately double (inactual fact, it is in the order of 1.8 to 2.1), by principally emittingsecond order diffracted light from the diffraction optical element 85when handling the high density optical disks (when using the first lightbeam of the first wavelength λ1) and by principally emitting first orderdiffracted light from the diffraction optical element 85 when handlingoptical disks such as CDs and CD-Rs (when using the third light beam ofthe third wavelength λ3), then a high diffraction efficiency can beobtained with respect to either wavelength even if the diffractionoptical element 85 is disposed in the same light path, and as a result,an optical head device that is capable of achieving excellent opticalcharacteristics, is attained.

Furthermore, a diffraction angle of the diffraction optical element isdetermined by the wavelength, the frequency and the diffraction order,however in the first conventional example, by using mainly second orderdiffracted light at the first wavelength λ1, and using mainly firstorder diffraction light at the third wavelength λ3, which has awavelength substantially twice as long, the same diffracting angle canbe set, even if the wavelength differs.

The cross-section of the diffraction optical element is substantiallysaw tooth-shaped. In the case of a transparent-type element in the firstconventional example, the depth h of the saw tooth-shape is set suchthat it is practically within the range from h1=2λ1/(n−1) to h3=λ3/(n−1)with respect to the first wavelength λ1, the third wavelength λ3 and therefractive index n of the material of the diffraction optical element85, such that the diffraction efficiency is large for all of thewavelengths. For example, if λ1=400 nm, λ3=800 nm and n=1.5, thenbecause h1=h3, with the transparent type element, h=1.6 μm.

Moreover, in the first conventional example, a case is also disclosed inwhich DVDs, which are optical disks of higher density than CDs, can beinterchangeably recorded and reproduced by also providing a laser lightsource that emits a light beam of a second wavelength λ2, which has awavelength substantially 1.5 times that of the light beam of the firstwavelength λ1. In this case, a single, or a plurality of diffractionoptical elements are disposed in the light path of the three wavelengthlight beam. The diffraction optical element principally emits sixthorder diffraction light with respect to the light beam of the firstwavelength λ1, principally emits third order diffraction light withrespect to the light beam of the third wavelength λ3, and principallyemits fourth order diffraction light with respect to the light beam ofthe second wavelength λ2.

In the first conventional example, it seems that the second wavelengthλ2 that is capable of recording and reproducing DVDs satisfies therelationship 570 nm≦λ2≦680 nm. However, from the ease of manufacture ofsemiconductor laser light sources, it is preferable that the secondwavelength λ2 is set to 650 nm to 680 nm, and in actual commerciallyavailable DVD optical information apparatuses, wavelengths of 650 nm to680 nm are used, with 660 nm as the standard.

Furthermore, due to the ease of manufacture of the semiconductor lasersit is also preferable that the first wavelength λ1 for optical disks ofan even higher density than next generation DVDs is set to 400 nm to 410nm, with 405 nm as the standard.

Using laser light sources having the first wavelength λ1 and the secondwavelength λ2, it is useful to use diffraction optical elements forcorrecting chromatic aberrations and the like, even in optical systemsin which DVDs, and optical disks of a higher density than the nextgeneration DVDs are recorded and reproduced.

BK7 glass is widely used as a material for the diffraction opticalelement. The refractive index n1 of BK7 is approximately 1.5302 withrespect to the first light beam of the first wavelength λ1=405 nm.

Setting the cross-section grating shape of the diffraction opticalelement to be saw tooth-shaped, in order to achieve a diffractiongrating whose second order diffraction efficiency is substantially 100%,as in the first conventional example, the depth h of the saw tooth shape(the height of the saw tooth) is:h=2λ1/(n1−1)=1530 nm.

Furthermore, the refractive index n2 of BK7 is approximately 1.5142 withrespect to the second light beam of the second wavelength λ2=660 nm.Thus, the light path difference that the depth of the saw tooth shape(the height of the saw tooth) h applies to the second light beam of thesecond wavelength λ2 is: $\begin{matrix}{{h( {{2n} - 1} )} = {786\quad{nm}}} \\{= {1.19\quad\lambda\quad 2}}\end{matrix}$Thus, because the light path difference that the depth of the saw toothshape (the height of the saw tooth) h applies to the second light beamof the second wavelength λ2 is not an integer multiple of the secondwavelength λ2, the second order diffraction efficiency decreases, andeven the first order diffraction efficiency is about 80%.

Setting the cross-section grating shape of the diffraction opticalelement to be saw tooth-shaped, in order to achieve a diffractiongrating whose sixth order diffraction efficiency is substantially 100%,as in a further embodiment disclosed according to the first conventionalexample, the depth h of the saw tooth shape (the height of the sawtooth) is:h=6λ1/(n1−1)=4580 nm.Thus, the light path difference that the depth of the saw tooth shape(the height of the saw tooth) h applies to the second light beam of thesecond wavelength λ2 is: $\begin{matrix}{{h( {{2n} - 1} )} = {2357\quad{nm}}} \\{= {3.57\quad\lambda\quad 2.}}\end{matrix}$In this manner, because the light path difference that the depth of thesaw tooth shape (the height of the saw tooth) h applies to the secondlight beam of the second wavelength λ2 is not an integer multiple of thesecond wavelength λ2, the sixth order diffraction efficiency decreasesand even the third order diffraction efficiency and the fourth orderdiffraction efficiency are lower than 60%. Furthermore, the loss becomesa scattered light component, and it is impossible to deny that this is acause of degradation in signal quality. Moreover, even if the materialis changed, there is not a big difference in scattering characteristics,so that even if a different material is selected, it cannot be expectedthat there will be a noticeable improvement.

Thus, as given above, the first conventional example has a problem inthat the light usage efficiency is low when the second light beam of thesecond wavelength λ2 is used when interchanging DVDs.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to solve the problems of theconventional art, and to provide optical head devices and opticalinformation apparatuses that use such optical head devices that arecapable of realizing interchangeable recording and interchangeablereproduction of a plurality of different types of optical informationmedia, and to provide various systems applying the optical informationapparatuses.

To achieve the object described above, a configuration of the opticalhead device according to the present invention provides one or pluralityof laser light sources for emitting a first light beam of a firstwavelength λ1 (400 nm to 415 nm) and a second light beam of a secondwavelength λ2 (650 nm to 680 nm), an objective lens for focusing thefirst and second light beams that are emitted from the laser lightsource respectively onto first and second optical information media, anda diffraction optical element arranged in a light path of the first andsecond light beams, wherein the diffraction optical element principallyemits 5N-th order diffracted light (N is a natural number) with respectto the first light beam, and principally emits 3N-th order diffractedlight with respect to the second light beam.

Furthermore, in the configuration of the optical head device accordingto the present invention, it is preferable that the laser light sourcefurther emits a third light beam of a third wavelength λ3 (780 nm to 810nm), and the third light beam is focused on a third optical informationmedium by the objective lens and that the diffraction optical elementprincipally emits 5M-th order diffracted light (2M=N) with respect tothe third light beam.

Furthermore, in the configuration of the optical head device accordingto the present invention, it is preferable that the diffraction opticalelement acts as a convex lens.

Furthermore, in the configuration of the optical head device accordingto the present invention, it is preferable that the diffraction opticalelement is disposed close to the objective lens, and that thediffraction optical element and the objective lens are fixed as a singlepiece.

Furthermore, a configuration of an optical information apparatusaccording to the present invention provides the optical head deviceaccording to the present invention, an optical information medium driveportion for driving the optical information medium, and a controlportion for receiving a signal obtained from the optical head device,and based on that signal, for controlling the optical information mediumdrive portion as well as the laser light source and the objective lensin the optical head device.

Furthermore, a configuration of a computer according to the presentinvention provides the optical information apparatus according to, thepresent invention, an input device for inputting information, aprocessing unit for processing based on information input from the inputdevice and/or information read out by the optical information apparatus,and an output device for display or output of the information input bythe input device, information read out by the optical informationapparatus, or a result processed by the processing unit.

Further, a configuration of an optical disk player according to thepresent invention provides the optical information apparatus accordingto the present invention, and an information-to-image conversionapparatus for converting the information signal obtained from theoptical information apparatus to an image.

Furthermore, a configuration of a car navigation system according to thepresent invention provides the optical disk player according to thepresent invention.

Furthermore, a configuration of an optical disk recorder according tothe present invention provides the optical information apparatusaccording to the present invention, and an image-to-informationconversion apparatus for converting image information to information forrecording onto the optical information medium by the optical informationapparatus.

Furthermore a configuration of an optical disk server according to thepresent invention provides the optical information apparatus accordingto the present invention, and a wireless input/output terminal forexchanging information between the optical information apparatus and anexternal portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural overview showing an optical head device accordingto a first embodiment of the present invention;

FIG. 2 is a cross-section view of an enlarged part of a diffractionoptical element according to the first embodiment of the presentinvention;

FIG. 3 is a structural overview of the optical head device according toa second embodiment of the present invention;

FIG. 4 is a structural view of another optical head device according toan embodiment of the present invention;

FIG. 5 is a structural overview of an optical information apparatusaccording to a third embodiment of the present invention;

FIG. 6 is a perspective overview showing a computer according to afourth embodiment of the present invention;

FIG. 7 is a perspective overview showing an optical disk playeraccording to a fifth embodiment of the present invention;

FIG. 8 is a perspective overview showing an optical disk recorderaccording to a sixth embodiment of the present invention;

FIG. 9 is a perspective overview showing an optical disk serveraccording to a seventh embodiment of the present invention;

FIG. 10 is a cross-section overview showing the basic structure andlight transmission state of an optical head device according to thefirst conventional example.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described below further, and in greater detailusing the embodiments.

FIRST EMBODIMENT

FIG. 1 is a structural overview showing an optical head device accordingto a first embodiment of the present invention. In FIG. 1, numeral 1indicates a first laser light source that emits a first light beam of afirst wavelength λ1, and numeral 2 indicates a second laser light sourcethat emits a second light beam of a second wavelength λ2. Numeral 7indicates a collimator lens (a first convex lens), numeral 20 indicatesa mirror for bending the light axis, and numeral 18 indicates anobjective lens. Numeral 8 indicates a diffraction optical element thatcompensates for wavelength fluctuations of the first laser light source1 that occur when there is a change in output intensity, and thatreduces the amount of shift in the focal position (chromatic aberration)caused by the objective lens 18. The diffraction optical element 8functions as a convex lens. Numerals 9 and 10 indicate an opticalinformation medium such as an optical disk or an optical card, howeverin the explanations given below, the example of an optical disk as theoptical information medium will be used.

It is preferable that some or all of the first and second laser lightsources 1 and 2 are semiconductor laser light sources, thereby achievingmore compact, lighter and more energy efficient optical head devices,and optical information apparatuses that use such devices. Here, thewavelength of the first laser light source 1 is the shortest, and thewavelength of the second laser light source 2 is longer than thewavelength of the first laser light source 1. The first laser lightsource 1 is used when recording and reproducing the highest recordingdensity optical disk 9, whereas the second laser light source is usedwhen recording and reproducing the lower recording density optical disk10. In this case, because the wavelengths of the first and the secondlaser light sources 1 and 2 are defined as λ1=400 nm to 415 nm, andλ2=650 nm to 680 nm, thus presently commercially available DVDs andoptical disks, which have even higher recording densities than DVDs, canbe interchangeably recorded and reproduced.

The optical disk 9 with the highest recording density is recorded andreproduced by focusing the first light beam that is emitted from thefirst laser light source 1 onto the information recording surface (notillustrated) of the optical disk 9 as described below. That is to say,the first light beam of the first wavelength λ1 that is emitted from thefirst laser light source passes through a wavelength selecting film (adichroic film) 5, passes substantially completely through a beamsplitter film 6, and is then converted to circularly polarized light bya ¼ wavelength plate 37. The first light beam that was converted tocircularly polarized light by the ¼ wavelength plate 37 is converted tosubstantially parallel light by the collimator lens 7, and is thendiffracted by the diffraction optical element 8. The first light beamthat was diffracted by the diffraction optical element 8 has its lightaxis bent by the mirror 20, after which it passes through a transparentsubstrate of the optical disk 9, which has a substrate thickness ofapproximately 0.1 mm, and is focused on the information recordingsurface by the objective lens 18.

The first light beam that is reflected by the information recordingsurface of the optical disk 9 passes back along the light path (returnpath), is diffracted again by the diffraction element 8, and is thenconverted by the ¼ wavelength plate 37 to linearly polarized light thatis polarized in a direction perpendicular to its initial polarizingdirection. The first light beam that was converted to linearly polarizedlight that is polarized in a direction perpendicular to its initialpolarizing direction is substantially completely reflected by the beamsplitter film 6, and passes through a detecting lens 12 to be incidenton a photodetector 13. Thus, it is possible to obtain the servo signalused in focus control and tracking, and the information signal, bycalculating the output strength from the photodetector 13. As describedabove, with regard to the first light beam of the first wavelength λ1and the second light beam of the second wavelength λ2, the beam splitterfilm 6 is a polarization separation film that allows linearly polarizedlight that is polarized in a predetermined direction to completely pass,and to completely reflect all light that is linearly polarized in adirection perpendicular to it.

It should be noted that, by also disposing a diffraction grating 4 inthe optical path from the first laser light source 1 to the beamsplitter film 6, it is possible to detect a tracking error signal by themethod that is known in the art as the difference push pull (DPP)method.

Furthermore, instead of converting the first light beam to substantiallyparallel light with the collimator lens 7, it is also possible toprovide a configuration in which the first light beam is converted togently diverging light by a first convex lens 7 and the first light beam(the gently diverging light) is further converted to substantiallyparallel light by a second convex lens 22. Thus, in this case, by movingthe second convex lens 22 in the direction of the light axis(horizontally, in FIG. 1) with a driving apparatus 23, the degree ofparallelism of the first light beam can be changed. Incidentally,spherical aberrations occur when there is unevenness in the substratethickness caused by discrepancies in the thickness of the transparentsubstrate, or when differences in substrate thickness are caused byinterlayer thicknesses if the optical disk 9 is a double layer disk.However, it is possible to compensate for the spherical aberrations bymoving the second convex lens 22 in the direction of the light axis asdescribed above. By moving the second convex lens 22 in a manner such asis given above, about several hundreds of mλ of compensation forspherical aberrations can be made possible if the numerical aperture(NA) of the focusing light is 0.85 with regard to the optical disk 9,thereby compensating for a substrate thickness difference of ±30 μm.

Here, it is also possible to achieve a reduction in the number of partsby forming the diffraction optical element 8 on the surface of thecollimator lens (first convex lens) 7 or on the second convex lens 22.

Furthermore, if the light axis bending mirror 20 is constituted suchthat it is not a totally reflecting mirror, but is a semi-transparentfilm that passes at most 20% of the amount of light of the first lightbeam, such that it guides the part of the first light beam that passedthe mirror 20 to the photodetector 21 by a focusing lens (convex lens)19, then it is possible to monitor changes in the amount of lightemitted by the first laser light source 1 by using both the signalobtained from the photodetector 21 to feed back changes in the amount oflight emitted, and to keep the amount of light emitted by the firstlaser light source 1 constant.

It should be noted that in the description above, the term “focus” wasused, however in the present specification, “focus” means “converging alight beam to a minute spot at the diffraction limit”.

Recording and reproduction of the second highest recording densityoptical disk 10 is performed by focusing the second light beam that isemitted from the second laser light source 2 onto an informationrecording surface (not shown) of the optical disk 10, as describedbelow. That is to say, the substantially linearly polarized second lightbeam of the second wavelength λ2 that is emitted from the second laserlight source 2 is reflected by the wavelength selecting film (dichroicfilm) 5 and further passes through the beam splitter film 6. The secondlight beam that has passed through the beam splitter film 6 is convertedto circularly polarized light by the ¼ wavelength plate 37, is convertedto substantially parallel light by the collimator lens 7, and is thendiffracted by the diffraction optical element 8. The second light beamthat was diffracted by the diffraction optical element 8, has its lightaxis bent by the mirror 20, after which it passes through thetransparent substrate of the optical disk 10, which has a substratethickness=approximately 0.6 mm, and is focused onto the informationrecording surface by the objective lens 18.

The second light beam that was reflected by the information recordingsurface of the optical disk 10 returns along the original optical path(return path), is again diffracted by the diffraction optical element 8,and is then reflected by the beam splitter film 6, passing through thedetecting lens 12 to be incident on the photodetector 13. Thus, theservo signals used in focus control and tracking control, and theinformation signal, can be obtained by calculating the power output fromthe photodetector 13.

It should be noted that, by also disposing a diffraction grating 15 inthe optical path from the second laser light source 2 to the beamsplitter film 6, it is possible to detect a tracking error signal by themethod that is known in the art as the difference push pull (DPP)method.

Furthermore, as described above, instead of converting the second lightbeam to substantially parallel light with the collimator lens 7, it isalso possible to provide a configuration in which the second light beamis converted to gently diverging light by the first convex lens 7 andthe second light beam (the gently diverging light) is further convertedto substantially parallel light by a second convex lens 22. Thus, inthis case, by causing the second convex lens 22 to move in the directionof the light axis (horizontally, in FIG. 1) by a driving apparatus 23,the degree of parallelism of the second light beam can be changed.Incidentally, spherical aberrations occur when there is unevenness inthe substrate thickness caused by discrepancies in the thickness of thetransparent substrate, or when differences in substrate thickness arecaused by interlayer thicknesses if the optical disk 10 is a doublelayer disk, however it is possible to compensate for the sphericalaberrations with a minimum of additional parts by employing a mechanismfor moving the second convex lens 22 in the direction of the light axis,as described above.

Furthermore, if the light axis bending mirror 20 is constituted suchthat it is not a totally reflecting mirror, but is a semi-transparentfilm that passes at most 20% of the amount of light of the second lightbeam, such that it guides the part of the second light beam that passedthe mirror 20 to the photodetector 21 by a focusing lens (convex lens)19, then it is possible to monitor changes in the amount of lightemitted by the second laser light source 2 by using both the signalobtained from the photodetector 21 to feed back changes in the amount oflight emitted, and to keep the amount of light emitted by the secondlaser light source 2 constant.

Furthermore, in the present embodiment, the first and second laser lightsources 1 and 2, which are separate devices, are configured so as toemit respectively the first light beam of the first wavelength λ1 andthe second light beam of the second wavelength λ2, however it is alsopossible to use a single chip laser light source to emit the first andsecond light beams, thus achieving a reduction in the number of parts.

Next, the lattice shape of the diffraction optical element 8 will bedescribed with reference to FIG. 2. FIG. 2 is a cross-section view of anenlarged part of a diffraction optical element according to the firstembodiment of the present invention. As shown in FIG. 2, when a latticepitch of the transmitting-type diffraction optical element 8 is set to p(constant) and a height of the saw tooth-shaped blaze shape is set to h(constant), generally, with respect to incident light (parallel light)16 of wavelength λ, diffracted light 17 is generated in a direction inwhich the wave path difference L is an integer multiple of thewavelength λ. In this case, when the wave path difference applied by theheight h of the saw tooth-shaped blaze form is equal to the light pathdifference L, diffraction efficiency is maximal, and this is theprincipal diffractive order. When the refractive index of the materialconstituting the diffraction optical element 8 is n, this condition canbe expressed as:L=h(n−1).

The inventors of the present invention have found that, in contrast tothe first conventional example, by configuring the saw tooth-shapedblazed hologram (the diffraction optical element 8) as shown in FIG. 2,such that the first light beam of the first wavelength λ1 (400 nm to 415nm) is emitted at principally 5N-th order diffracted light (where N is anatural number), and the second light beam of the second wavelength λ2(650 nm to 680 nm) is emitted at principally 3N-th order diffractedlight, a high diffraction efficiency with respect to the light beams ofboth wavelengths can be can be simultaneously achieved. For example, byconfiguring the diffraction optical element such that the first lightbeam of the first wavelength λ1 (400 nm to 415 nm) is emitted atprincipally 5th order diffracted light, and the second light beam of thesecond wavelength λ2 (650 nm to 680 nm) is emitted at principally 3rdorder diffracted light, a high diffraction efficiency can be can besimultaneously achieved with respect to the light beams of bothwavelengths. This is described below.

If the saw tooth-shaped blazed hologram as shown in FIG. 2 is formedfrom glass (BK7), then in order to maximize the fifth order diffractionefficiency of the first light beam of the first wavelength λ1 (standardvalue 405 nm), it is preferable that the light path difference, which isdependent on the height h of the saw tooth-shaped blaze shape, is set tofive times the first wavelength λ1 and thus the height h of the sawtooth-shaped blaze shape is optimally set to: $\begin{matrix}{h = {5\quad\lambda\quad{1/( {{n\quad 1} - 1} )}}} \\{= {3820\quad{{nm}.}}}\end{matrix}$Here, n1 is the refractive index of BK7 with respect to the firstwavelength λ1=405 nm, and is approximately 1.5302.

Furthermore, the diffracting pattern can be designed by assuming thewavelength λ is five times the first wavelength λ1.

At this time, the light path difference that the saw tooth-shaped blazeshape of height h applies to the second light beam of the secondwavelength λ2 (standard value 660 nm) for recording on or reproducingfrom DVDs, is: $\begin{matrix}{{h( {{2n} - 1} )} = {1964\quad{nm}}} \\{= {2.98\quad\lambda\quad 2.}}\end{matrix}$In this manner, because the light path difference, which the height h ofthe saw tooth-shaped blaze shape applies to the second light beam of thesecond wavelength λ2 for the purpose of recording or reproducing DVDs issubstantially three times the second wavelength λ2, the 3rd orderdiffraction efficiency can be set to substantially 100%. Here, n2 is therefractive index of BK7 with respect to the second wavelength λ2=660 nm,and is approximately 1.5142.

As for the scattering characteristics, because there is not a largedifference even if the materials are changed, then the same effect canbe obtained even if another material is selected for the diffractionoptical element 8, such as plastic (resin).

Thus, in an optical head device provided with a single or a plurality oflaser light sources for emitting the first light beam of the firstwavelength λ1 (400 nm to 415 nm) and the second light beam of the secondwavelength λ2 (650 nm to 680 nm), and an objective lens for focusing thefirst and second light beams that are emitted from the laser lightsource respectively on to the first and second optical informationmedia, by further providing a diffraction optical element in the lightpaths of the first and second light beams that principally emit 5N-thorder diffracted light (where N is a natural number) with respect to thefirst light beam and principally emits 3N-th order diffracted light withrespect to the second light beam, a high diffraction efficiency ofsubstantially 100% can be simultaneously achieved with respect to bothlight beams. Consequently, high light usage efficiency can be achievedwhen recording or reproducing DVDs, and when recording or reproducingoptical disks that have even higher recording and reproductiondensities. Furthermore, it is also possible to achieve optical headdevices that have no noise generated by stray light from needlesslydiffracted light, and that have low power consumption and low heatgeneration.

SECOND EMBODIMENT

FIG. 3 is a structural overview of the optical head device according toa second embodiment of the present invention;

As shown in FIG. 3, by further providing a third laser light source 3 ofa third wavelength λ3=770 nm to 810 nm, optical disks such as CDs, whichhave transparent substrate material of a substrate thickness ofapproximately 1.2 mm, can be recorded or reproduced. It should be notedthat in FIG. 3, numeral 11 indicates an optical disk such as a CD withthe lowest recording density. Furthermore, numeral 14 indicates awavelength selection film (dichroic film) for passing the second lightbeam of the second wavelength λ2 and reflecting the third light beam ofthe third wavelength λ3. Because the other structures are the same as inthe first embodiment described above (see FIG. 1), the same structuralmembers are attached with the same symbols, and their furtherdescription has been hereby omitted.

The optical disk 11, which has the lowest recording density, is recordedand reproduced by focusing the third light beam that is emitted by thethird laser light source 3 onto the information recording surface (notshown) of the optical disk 11, as given below. That is to say that, asshown in FIG. 3, the substantially linearly polarized light of the thirdlight beam of the third wavelength λ3 (=770 nm to 810 nm, with astandard of 780 nm) that is emitted from the third laser light source 3is reflected by the wavelength selecting film (dichroic film) 14, afterwhich it is also reflected by the wavelength selecting film (dichroicfilm) 5 and passes through the beam splitter film 6. The third lightbeam that passed through the beam splitter film 6 is converted tosubstantially parallel light by the collimator lens 7, and is thendiffracted by the diffraction optical element 8. The third light beamthat was diffracted by the diffraction optical element 8 has its lightaxis bent by the mirror 20, after which it passes through thetransparent substrate of the optical disk 11 that has a substratethickness of 1.2 mm, and is focused onto the information recordingsurface by the objective lens 18.

The third light beam that was reflected by the information recordingsurface of the optical disk 11 returns along the original optical path(return path), is again diffracted by the diffraction optical element 8,and is then reflected by the beam splitter film 6, passing through thedetecting lens 12 to be incident on the photodetector 13. Thus, theservo signals used in focus control and tracking control, and theinformation signal, can be obtained by calculating the power output fromthe photodetector 13.

Furthermore, in the present embodiment, the first to third laser lightsources 1 to 3, which are separate devices, are configured so as to emitrespectively the first light beam of the first wavelength λ1, the secondlight beam of the second wavelength λ2, and the third light beam of thethird wavelength λ3, however it is also possible to use a single chiplaser light source to emit the first to third light beams, thusachieving a reduction in the number of parts.

The inventors of the present invention have found that, if the thirdlight beam of the third wavelength λ3 is further used in the manner ofthe present embodiment, in contrast to the first conventional example,by configuring the saw tooth-shaped blazed hologram (the diffractionoptical element 8) as shown in FIG. 2, such that the first light beam ofthe first wavelength λ1 (400 nm to 415 nm) is emitted at principally5N-th order diffracted light (where N is a natural number), the secondlight beam of the second wavelength λ2 (650 nm to 680 nm) is emitted atprincipally 3N-th order diffracted light, and the third light beam ofthe third wavelength λ3 (780 nm to 810 nm) is emitted at principally5M-th order diffracted light (2M=N, where M is a natural number) then ahigh diffraction efficiency can be can be simultaneously achieved withrespect to the light beams of the three wavelengths. For example, byconfiguring the diffraction optical element such that the first lightbeam of the first wavelength λ1 (400 nm to 415 nm) is emitted atprincipally 10th order diffracted light, the second light beam of thesecond wavelength λ2 (650 nm to 680 nm) is emitted at principally 6thorder diffracted light, and the third light beam of the third wavelengthλ3 (780 nm to 810 nm) is emitted at principally 5th order diffractedlight, a high diffraction efficiency can be simultaneously achieved withrespect to the light beams of the three wavelengths. This is describedbelow.

If the saw tooth-shaped blazed hologram as shown in FIG. 2 is formedfrom glass (BK7), then in order to maximize the tenth order diffractionefficiency of the first light beam of the first wavelength λ1 (standardvalue 405 nm), it is preferable that the light path difference, which isdependent on the height h of the saw tooth-shaped blaze shape, is set toten times the first wavelength λ1 and thus the height h of the sawtooth-shaped blaze shape is optimally set to: $\begin{matrix}{h = {10\quad\lambda\quad{1/( {{n\quad 1} - 1} )}}} \\{= {7640\quad{{nm}.}}}\end{matrix}$Here, n1 is the refractive index of BK7 with respect to the firstwavelength λ1=405 nm, and is approximately 1.5302.

Furthermore, the diffraction pattern can be designed by assuming thewavelength λ is ten times the first wavelength λ1.

At this time, the light path difference that the sawtooth-shaped blazeshape of height h applies to the second light beam of the secondwavelength λ2 (standard value 660 nm), which records on to or reproducesfrom DVDs, is: $\begin{matrix}{{h( {{2n} - 1} )} = {3928\quad{nm}}} \\{= {5.95\quad\lambda\quad 2.}}\end{matrix}$Thus, because the light path difference, which the height h of the sawtooth-shaped blaze shape applies to the second light beam of the secondwavelength λ2 for the purpose of recording or reproducing DVDs issubstantially six times the second wavelength λ2, the 6th orderdiffraction efficiency can be set to substantially 100%. Here, n2 is therefractive index of BK7 with respect to the second wavelength λ2=660 nm,and is approximately 1.5142.

Furthermore, the light path difference that the sawtooth-shaped blazeshape of height h applies to the third light beam of the thirdwavelength λ3 (standard value 780 nm), which records on to or reproducesfrom DVDs, is: $\begin{matrix}{{h( {{3n} - 1} )} = {3903\quad{nm}}} \\{= {4.94\quad\lambda\quad 3.}}\end{matrix}$Thus, because the light path difference, which the height h of the sawtooth-shaped blaze shape applies to the third light beam of the thirdwavelength λ3 for the purpose of recording or reproducing CDs issubstantially five times the third wavelength λ3, the 5th orderdiffraction efficiency can be set to substantially 100%. Here, n3 is therefractive index of BK7 with respect to the third wavelength λ3=780 nm,and is approximately 1.5110.

As for the scattering characteristics, because there is not a largedifference even if the materials are changed, then the same effect canbe obtained even if another material is selected for the diffractionoptical element 8, such as plastic (resin).

Thus, in an optical head device provided with a single or a plurality oflaser light sources for emitting the first light beam of the firstwavelength λ1 (400 nm to 415 nm), the second light beam of the secondwavelength λ2 (650 nm to 680 nm), the third light beam of the thirdwavelength λ3 (780 nm to 810 nm), and an objective lens for focusing thefirst to third light beams that are emitted from the laser light sourcesrespectively on to the first to third optical information media, byfurther providing a diffraction optical element in the light paths ofthe first to third light beams for principally emitting 5N-th orderdiffracted light (where N is a natural number) with respect to the firstlight beam, for principally emitting 3N-th order diffracted light withrespect to the second light beam, and for principally emitting 5M-thorder diffracted light (2M=N, where M is a natural number) with respectto the third light beam, then a high diffraction efficiency ofsubstantially 100% can be simultaneously achieved with respect to thethree light beams. Consequently, high light usage efficiency can beachieved when recording or reproducing CDs, DVDs and optical disks,which have even higher recording and reproduction densities.Furthermore, it is also possible to achieve optical head devices thathave no noise generated by stray light from needlessly diffracted light,as well as having low power consumption and low heat generation.

It should be noted that the diffraction optical element 8 according tothe first and second embodiments described above is an element thatallows transmission of the first light beam of the first wavelengthλ1=400 nm to 415 nm. Generally, the shorter the wavelength of light, thehigher the photon energy, and as a result, there is a tendency towardchanges in material properties, and to a deterioration in transmittanceand mechanical strength. Consequently, it is preferable that thediffraction optical element 8 is constituted by material with a lowabsorptance with respect to the first light beam of the first wavelengthλ1=400 nm to 415 nm. For example, material degradation caused byabsorption of photonic energy can be prevented by a material that isapproximately 5 mm thick, whose transmittance with respect to the firstlight beam of the first wavelength λ1 is high, and whose absorptance isnot more than 5%. Moreover, high reliability can be obtained by using amaterial that is approximately 5 mm thick, and whose absorptance of thefirst light beam of the first wavelength λ1 is not more than 3%.Consequently, it is preferable to use an inorganic glass material suchas quartz as the material for constituting the diffraction opticalelement 8. Furthermore, it is also possible to use a resin material,whose advantages are excellent processability and light weight, as thematerial that constitutes the diffraction optical element 8, however inthis case, it is preferable to use material such as amorphouspolyolefins that have low absorptance of the first light beam of thefirst wavelength λ1.

Furthermore, as shown in FIG. 4, by configuring the diffraction opticalelement 8, which is described according to the first and secondembodiments, such that the optical element 8 is disposed in the vicinityof the objective lens 18 and is fixed to the objective lens 18 as asingle piece, the diffraction optical element 8 and the objective lens18 can be driven as a single piece by the drive apparatus 36 duringfocus control and tracking control, and the following effect can beachieved. That is to say, it is possible to suppress the occurrence ofaberrations even if the objective lens 18 moves due to tracking duringrecording or reproduction of the optical disks 9 to 11, because axialdisplacement of the diffraction optical element 8 and the objective lens18 can be prevented. Furthermore, although the grating pitch of thediffraction optical element 8 becomes finer toward the outercircumferential portion, if the configuration such as described above isemployed, then because there is no necessity to redundantly make theouter circumferential portion of the diffraction optical grating,fabrication of the diffraction optical element is simplified.

Furthermore, the diffraction optical element 8 shown in the first andsecond embodiments described above is not limited to an optical elementfor the correction of chromatic aberrations, but can also be used as anoptical element for formation of light for detecting the servo signalused in conjunction with the detection lens 12, and in this case, asimilar effect can be obtained as is described above.

THIRD EMBODIMENT

FIG. 5 is a structural overview of an optical information apparatusaccording to a third embodiment of the present invention. As shown inFIG. 5, the optical disk 10 (or 9 or 11, this is the same below) isrotatably driven by an optical disk drive portion 52 that is providedwith a motor or the like (if an optical card is used in place of theoptical disk 10, then the card is translatably driven). Numeral 55indicates the optical head device shown in the first and secondembodiments, and the optical head device 55 is coarsely adjusted by anoptical head device drive apparatus 51 to where the track containing thedesired information is present on the optical disk 10.

Furthermore, the optical head device 55 sends a focus error signal andtracking error signal to an electric circuit 53, which acts as a controlportion, in accordance with the positional relationship with the opticaldisk 10. The electric circuit 53 sends signals for the purpose of finecontrolling the objective lens to the optical head device 55 inaccordance with these signals. Thus, based on these signals, the opticalhead device 55 carries out focus control and tracking control of theoptical disk 10, and then reads, records or erases information.Furthermore, the electric circuit 53 also controls the optical diskdrive portion 52 and the laser light sources within the optical headdevice 55 in accordance with the signals obtained from the optical headdevice 55. It should be noted that in FIG. 5 numeral 54 indicates apower source or a connecting portion to an external power source.

In the optical information apparatus 50 of the present embodiment, usingthe optical head device 55, high light usage efficiency can be achievedwhen recording or reproducing DVDs, which are illustrated in the firstand second embodiments described above, and optical disks that have evenhigher recording and reproduction densities. Furthermore, because theoptical head device of the present invention, which has no noisegenerated by stray light from needlessly diffracted light, as well ashaving low energy consumption and low heat generation, is used, it ispossible to achieve an optical information apparatus capable ofaccurately and stably reproducing information, and whose powerconsumption and thermal generation are low.

FOURTH EMBODIMENT

FIG. 6 is a perspective view that schematically shows a computeraccording to the fourth embodiment of the present invention.

As shown in FIG. 6, a computer 60 according to the present embodiment isconstituted by the optical information apparatus 50 of the thirdembodiment described above, an input device 65 for the purpose ofinputting information, such as a keyboard, a mouse, or a touchpanel, aprocessing unit 64 such as central processing unit (CPU) for the purposeof processing in accordance with information input from the input device65 via an input cable 63 or read out from the optical informationapparatus 50, an output device 61 such as a cathode ray tube, liquidcrystal display or printer, for the purpose of displaying or outputtingthe information input from the input device 65, the information read outfrom the optical information apparatus 50 or the information that was aresult calculated by the processing unit 64. It should be noted that inFIG. 6, numeral 62 indicates an output cable for the purpose ofoutputting information to the output device 61 such as the resultscalculated by the processing unit 64.

FIFTH EMBODIMENT

FIG. 7 is a perspective view that schematically shows an optical diskplayer according to the fifth embodiment of the present invention.

As shown in FIG. 7, an optical disk player 67 according to the presentembodiment is provided with an optical information apparatus 50according to the third embodiment, and an information-to-imageconversion device (such as a decoder 66) for converting an informationsignal obtained from the optical information apparatus 50 into an image.

It should be noted that it is also possible to utilize the presentconfiguration as a car navigation system. By installing loading the carnavigation system of the present configuration into an automobile, aplurality of optical disks of different varieties can be stably recordedand reproduced inside the automobile. Furthermore, because powerconsumption is low, then without limitation to just car navigationsystems, it is possible to obtain the benefits of using the navigationsystem over a wide range of applications such as for listening to music,or watching movies. Furthermore, it is also possible to set thisconfiguration such that the output device 61 such as cathode raydevices, liquid crystal devices and printers are connected via theoutput cable 62.

SIXTH EMBODIMENT

FIG. 8 is a perspective view that schematically shows an optical diskrecorder according to the sixth embodiment of the present invention.

As shown in FIG. 8, an optical disk recorder 71 according to the presentembodiment is provided with the optical information apparatus 50according to the third embodiment, and an image-to-information converter(such as an encoder 68), for converting image information intoinformation for recording onto the optical disk by the opticalinformation apparatus 50.

It should be noted that it is possible to have a configuration thatincludes an information-to-image conversion device (such as the decoder66) that converts the information signal obtained from the opticalinformation apparatus 50 to images, and thus, it is possible tosimultaneously display on a monitor during recording to the opticaldisk, or to reproduce portions that are already recorded.

Furthermore, it is also possible to configure the optical disk recordersuch that output devices 61 such as cathode ray devices, liquid crystaldevices or printers are connected via the output cable 62.

Computers, optical disk players and optical disk recorders provided withthe optical information apparatus 50 described according to the thirdembodiment, or employing methods for recording and reproducing describedabove, are capable of stably recording or reproducing a plurality ofoptical disks of different varieties, and because power consumption islow, it is possible to use them in a wide range of applications.

SEVENTH EMBODIMENT

FIG. 9 is a perspective view that schematically shows an optical diskserver according to the seventh embodiment of the present invention.

As shown in FIG. 9, an optical disk server 70 of the present embodimentis provided with the optical information apparatus 50 described aboveaccording to the third embodiment, and an input/output wireless terminal(wireless input/output terminal) 69 that is a wireless receiving deviceand transmitting device for the purpose of reading in information froman external portion for recording to the optical information apparatus50, and for output to an external portion of information read out by theoptical information apparatus 50 (ie. for the purpose of exchanginginformation between the optical information apparatus 50 and an externalportion).

By the structure above, it is possible to utilize the optical diskserver 70 as a shared information server that exchanges information backand forth with devices that contain a plurality of wireless receivingand transmitting terminals, such as computers, telephones and televisiontuners. Furthermore, as a plurality of differing varieties of opticaldisks can be stably recorded and reproduced, the optical disk server 70can be used in a wide range of applications.

It should be noted that a configuration is also possible in which animage-to-information converting device (such as the encoder 68) is addedso as to convert the image information into information for recordingonto the optical disk by the optical information apparatus 50.

Furthermore, it is also possible to have a configuration in which aninformation-to-image converting device (such as the decoder 66) is addedthat converts the signal obtained from the optical information apparatus50 to images, and thus it is possible to simultaneously display on amonitor during recording to the optical disk, or reproduce portionsalready recorded.

Furthermore, it is also possible to configure the optical disk serversuch that output devices 61 such as cathode ray devices, liquid crystaldevices or printers are connected via the output cable 62.

Furthermore, according to the fourth to seventh embodiments, the outputdevice 61 is shown in FIGS. 6 to 9, but by simply providing an outputterminal without the output device 61, a merchandising model is alsopossible in which this is sold separately. Furthermore, input devicesare not shown in FIGS. 7 to 9, however a merchandising model is alsopossible in which input devices such as keyboards, mouses or touchpanelsare provided.

Furthermore, it is possible to obtain a similar effect as an opticaldisk even if an optical card is used as the optical information mediumaccording to the present invention, instead of the optical disk. That isto say, the present invention can be applied to all optical informationmedia that are recorded or reproduced by the formation of minute focusedspots.

1-10. (canceled)
 11. An optical head device, comprising: a first laserlight source for emitting a first light beam of a first wavelength λ1(400 nm to 415 nm); a second laser light source for emitting a secondlight beam of a second wavelength λ2 (650 nm to 680 nm); a focusingoptical system for focusing the first and second light beams that areemitted from the first and second laser light sources respectively, andforming minute spots on information recording surfaces of first andsecond optical information media; and a photodetector for receiving thefirst and second light beams reflected respectively by the informationrecording surfaces of the first and second optical information media tooutput an electric signal in accordance with light amounts of the firstand second light beams; wherein a common spherical aberration correctionelement is disposed in light paths of the first and second light beams,and spherical aberrations of the minute spots are controlled by thespherical aberration correction element.
 12. The optical head deviceaccording to claim 11, wherein the spherical aberration correctionelement is a collimator lens for receiving the first and second lightbeams that are emitted from the first and second laser light sourcesrespectively to convert the first and second light beams tosubstantially parallel light beams, and a control mechanism, in whichspherical aberrations of the minute spots are controlled by moving thecollimator lens in the direction of the light axis, is provided.
 13. Anoptical information apparatus, comprising: the optical head deviceaccording to claim 11; an optical information medium drive portion fordriving the optical information medium; and a control portion forreceiving a signal obtained from the optical head device, and forcontrolling the optical information medium drive portion.
 14. Acomputer, comprising: the optical information apparatus according toclaim 13; an input device for inputting information; a processing unitfor processing based on information input from the input device and/orinformation read out by the optical information apparatus; and an outputdevice for display or output of the information input by the inputdevice, information read out by the optical information apparatus, or aresult processed by the processing unit.
 15. An optical disk player,comprising: the optical information apparatus according to claim 13; andan information-to-image conversion apparatus for converting theinformation signal obtained from the optical information apparatus to animage.
 16. An optical disk recorder, comprising: the optical informationapparatus according to claim 13; and an image-to-information conversionapparatus for converting image information to information for recordingonto the optical information medium by the optical informationapparatus.
 17. An optical head device, comprising: a first laser lightsource for emitting a first light beam of a first wavelength λ1 (400 nmto 415 nm); a second laser light source for emitting a second light beamof a second wavelength λ2 (650 nm to 680 nm) an objective lens forfocusing the first light beam that is emitted from the first laser lightsource, and forming minute spot on a first information recording surfaceof a first optical information medium; and a photodetector for receivingthe first light beam reflected by the information recording surface ofthe first optical information medium to output an electric signal inaccordance with light amount of the first light beams; wherein a commonspherical aberration correction element is disposed in light paths ofthe first and second light beams, and spherical aberration of the minutespot is controlled by the spherical aberration correction element. 18.The optical head device according to claim 17, wherein the sphericalaberration correction element is a collimator lens for receiving thefirst and second light beams that are emitted from the first and secondlaser light sources respectively to convert the first and second lightbeams to substantially parallel light beams, and a control mechanism, inwhich spherical aberration of the minute spot is controlled by movingthe collimator lens in the direction of the light axis, is provided. 19.The optical head device according to claim 17, wherein the objectivelens focuses the second light beam that is emitted from the second laserlight source, and forms minute spot on a second information recordingsurface of a second optical information medium.
 20. The optical headdevice according to claim 19, wherein the first light beam passesthrough a transparent substrate of substrate thickness Ti and is focusedon the first information recording surface of the first opticalinformation recording medium, and the second light beam passes through atransparent substrate of substrate thickness T2 and is focused on thesecond information recording surface of the second optical informationrecording medium, and the substrate thicknesses Ti and T2 satisfy therelationship of Ti<T2.
 21. The optical head device according to claim19, further comprising a third laser light source for emitting a thirdlight beam of a third wavelength λ3 (780 nm to 810 nm), wherein theobjective lens focuses the third light beam that is emitted from thethird laser light source, and forms minute spot on a third informationrecording surface of a third optical information medium.
 22. An opticalinformation apparatus, comprising: the optical head device according toclaim 17; an optical information medium drive portion for driving theoptical information medium; and a control portion for receiving a signalobtained from the optical head device, and for controlling the opticalinformation medium drive portion.
 23. A computer, comprising: theoptical information apparatus according to claim 22; an input device forinputting information; a processing unit for processing based oninformation input from the input device and/or information read out bythe optical information apparatus; and an output device for display oroutput of the information input by the input device, information readout by the optical information apparatus, or a result processed by theprocessing unit.
 24. An optical disk player, comprising: the opticalinformation apparatus according to claim 22; and an information-to-imageconversion apparatus for converting the information signal obtained fromthe optical information apparatus to an image.
 25. An optical diskrecorder, comprising: the optical information apparatus according toclaim 22; and an image-to-information conversion apparatus forconverting image information to information for recording onto theoptical information medium by the optical information apparatus.
 26. Anoptical head device, comprising: a first laser light source for emittinga first light beam of a first wavelength λ1 (400 nm to 415 nm); acollimator lens for receiving the first light beam that is emitted fromthe first laser light source to convert the first light beam tosubstantially parallel light beam; an objective lens for focusing thefirst light beam that is converted to substantially parallel light beamby the collimator lens, and forming minute spot on a first informationrecording surface of a first optical information medium; and aphotodetector for receiving the first light beam reflected by theinformation recording surface of the first optical information medium tooutput an electric signal in accordance with light amount of the firstlight beams; wherein a diffraction optical element acts as a convex lensis disposed close to the collimator lens in light path of the firstlight beam, thereby reducing chromatic aberration of the objective lens,and a control mechanism, in which spherical aberration of the minutespot is controlled by moving the collimator lens in the direction of thelight axis, is provided.
 27. An optical information apparatus,comprising: the optical head device according to claim 26; an opticalinformation medium drive portion for driving the first opticalinformation medium; and a control portion for receiving a signalobtained from the optical head device, and for controlling the opticalinformation medium drive portion.
 28. A computer, comprising: theoptical information apparatus according to claim 27; an input device forinputting information; a processing unit for processing based oninformation input from the input device and/or information read out bythe optical information apparatus; and an output device for display oroutput of the information input by the input device, information readout by the optical information apparatus, or a result processed by theprocessing unit.
 29. An optical disk player, comprising: the opticalinformation apparatus according to claim 27; and an information-to-imageconversion apparatus for converting the information signal obtained fromthe optical information apparatus to an image.
 30. An optical diskrecorder, comprising: the optical information apparatus according toclaim 27; and an image-to-information conversion apparatus forconverting image information to information for recording onto theoptical information medium by the optical information apparatus.